This invention relates to circuit breakers. More particularly, it is concerned with low voltage circuit breakers for controlling low and moderate power electrical circuits.
A circuit breaker for use in controlling electrical circuits typically has a set of contacts, one fixed and one movable, and a toggle, or overcenter mechanism, which is manually operated to close and open the contacts. A circuit breaker also includes an overload mechanism for tripping the circuit breaker and opening the contacts automatically when the electrical current through the circuit breaker exceeds certain predetermined conditions.
Typically circuit breakers of this type include an overcenter spring which is connected between a movable contact arm carrying the movable contact and a trip arm which is held latched in a set position under normal operating conditions. The contact arm pivots about a pivot point which is shiftable by means of a manually-operated handle to place the pivot point on one side of the overcenter spring whereby the spring causes the contacts to be closed, or to place the pivot point on the other side of the overcenter spring whereby the spring causes the contacts to be open. Under overload conditions a current sensitive mechanism releases the latched trip arm and the overcenter spring moves the trip arm from the set to a tripped position. Movement of the trip arm to the tripped position shifts the position of the overcenter spring with respect to the pivot point and the force of the overcenter spring in this position causes the contacts to open.
In certain situations the action of the overcenter spring alone after the trip arm has been released may not be adequate to separate the contacts or to separate them as rapidly as might be desired. Various mechanisms have been employed for positively urging the contacts apart to supplement the action of the overcenter spring arrangement. Mechanisms for this purpose are disclosed in U.S. Pat. No. 2,624,815 to Gano et al, for example. The arrangement of the mechanical elements in various types of circuit breakers, however, precludes the use of mechanisms such as those shown in the patent to Gano et al for positively separating the contacts. An example of one such form of circuit breaker is described in U.S. Pat. Nos. 3,089,933, 3,200,228, and 3,244,835 to Locher. In this circuit breaker the configurations of the trip arm and movable contact arm, their paths of movement with respect to each other, and the arrangement of other elements precludes employing the mechanism of Gano et al to positively open the contacts upon tripping.